Deployable nozzle extension for rocket engines

ABSTRACT

A deployable nozzle for rocket engines and method of making same is disclosed in which the extension initially is in collapsed state and is provided with a detachable cover so that internal pressure may be utilized to extend and deploy the extension. The extension includes an outer convolution of annular divergent frusto-conical form joined along a fold line to an intermediate convolution also of frusto-conical form but directed oppositely from the outer convolution and the intermediate convolution is joined at its small end to a divergent frusto-conical rocket nozzle portion through a relatively narrow cylindrical band which surrounds the divergent nozzle portion and is joined to it at a point spaced from the end of such nozzle portion. The length of this band is of predetermined relation with respect to the length of the free end portion of the nozzle extension such that when the nozzle extension is deployed, it will unroll over the edge of the free end of the nozzle extension to embrace it and form a non-offset and coplanar extension of the inner surface of the rocket nozzle portion.

United States Patent 91 Dueringer DEPLOYABLE NOZZLE EXTENSION FOR ROCKETENGINES [75] Inventor: John Wilbur Dueringer, Kenmore,

[73] Assignee: Textron, Inc., Providence, RI.

[22] Filed: May 22, 1972 [21] Appl. No.: 255,394

Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-John J. Love A"Way a s34 Bean lllllll Jan. 8, 1974 [5 7] ABSTRACT A deployable nozzlefor rocket engines and method of making same is disclosed in which theextension initially is in collapsed state and is provided with adetachable cover so that internal pressure may be utilized to extend anddeploy the extension. The extension includes an outer convolution ofannular divergent frusto-conical form joined along a fold line to anintermediate convolution also of frusto-conical form but directedoppositely from the outer convolution and the intermediate convolutionis joined at its small end to a divergent frusto-conical rocket nozzleportion through a relatively narrow cylindrical band which surrounds thedivergent nozzle portion and is joinedto it at a point spaced from theend of such nozzle portion. The length of this band is of predeterminedrelation with respect to the length of the free end portion of thenozzle extension such that when the nozzle extension is deployed, itwill unroll over the edge of the free end of the nozzle extension toembrace it and form a non-offset and coplanar extension of the innersurface of the rocket nozzle portion.

14 Claims, 9 Drawing Figures PATENTEUJAH 8IEI'I I 3.784.109

SHEET 3 BF 3 ROLLING PRESSURE-PSIG rx) 8 8 8 8% 8 8 8 I I I I II I FIG.9

DEPLOYABLE NOZZLE EXTENSION FOR ROCKET ENGINES CROSS REFERENCE TORELATED APPLICATION This application discloses subject matter related tothat described in copending application, Ser. No. 125,087, filed Mar.17, 1971, now U.S. Pat. No. 3,71 1,027 dated Jan. 16, 1973 and assignedin common herewith.

BACKGROUND OF THE INVENTION As is well known, the expansion ratio of arocket engine required for maximum thrust efficiency varies with theabsolute ambient pressure. In multi-stagerocket engines where a laterstage is to be fired in space or at high altitudes, the expansion ratiois relatively great and would require a divergent exit nozzle portion ofthe rocket engine which is of substantial length. However, to make asecond or later engine stage of such overall length as would be requiredto produce a reguisite expansion ratio would be extremely cumbersome andwasteful of otherwise usable space in the rocket assembly. Thus, it isdesirable to provide means associated with a rocket engine so that adivergent nozzle of a length suitable for maximum thrust at low ambientpressure may be obtained by deploying such means. In this way, therocket engine may be very compact so the entire assembly when storeddoes not add appreciably to the length of the normal combustion chamberand divergent nozzle portions of the rocket engine. The expansion ratioof such compact assembly may be increased to that greater value willrender the thrust efficient with zero or substantially zero ambientpressure simply by deploying the extension means. Numerous attempts havebeen made to provide such extensions and they may be broadly categorizedin either one or two classes. In the first class, the extension is madeof some flexible and essentially nonresilient material such as isdisclosed for example in U.S. pat. No. 3,596,465. The other class ofprior art extensions employs a series of frusto-conical sections whichare not joined but which are movable from a collapsed state to anextended state. This latter type employs metallic sections and isexemplified by U.S. Pat. No. 3,183,664.

Due to the materials used in the first mentioned class of nozzleextensions, it is extremely difficult to obtain sufficient cooling toprevent the extension when deployed from burning out. In the secondclass of extensions, it is extremely difficult to effect a good sealbetween the several frusto-conical sections and the means for deployingthem properly is inherently complex, cumbersome and heavy.

Unfortunately, the inherent problems of both of these classes of nozzleextensions are considerably magnified were they to be used with the morepowerful rocket engines currently being developed. The reason for thisis that more powerful engines employ substantially greater chamberpressure and temperature than previous rocket engines and this onlymagnifies the problems as discussed above.

To avoid the problems of the prior art, and to provide a deployablerocket nozzle extension which is of essentially uniform anduninterrupted construction when deployed and which provides a smoothinterior which is essentially a continuation of the rocket nozzleportion to which it is attached, the deployable nozzle extension of theaforesaid commonly assigned U.S. Pat. No.

3,711,027 was developed. The required frusto-conical extensionconfiguration producing the requisite half angle of the nozzle exit coneof this nozzle extension may be constructed by shear spinning it from asuitable circular blank of sheet metal. The extension may then betelescopically rolled back upon itself to provide an inner convolutionsurrounded by an outwardly spaced but parallel outer convolution joinedby a reversedirected intermediate convolution.

Alternatively, the three convolutions may be formed separately andjoined together as a unitary whole in the collapsed condition by meansof welding. In any event, the three sections are joined together so thatat least the outer and intermediate sections merge along a peripheral orannular fold and outer convolution may be closed by a cover. Byinternally pressurizing the rocket chamber, as by slow-starting it, thepressure reacting against the cover will cause the fold joining theouter convolution to the intermediate convolution preferentially tounroll until it reaches the juncture or the fold between theintermediate convolution and the inner convolution. Mechanical means mayalso be used for this purpose such as is shown for example in U.S. Pat.No. 3,346,186. Due to the fact that the unrolling action produces acertain amount of radial stretching of the metal, a certain amount ofradial offset will be produced between the inner convolution and theintermediate convolution at the point at which the two are joined.Although it is possible to exert sufficient force against the cover tostraighten out and stretch the material in this area so that asubstantially smooth and uninterrupted extension of the inner surface ofthe divergent end of the rocket engine is achieved, a certain amount ofradial offset will be produced in any case. Moreover, it is in generalundesirable to carry the force-exerting pressure to such an extreme.This is particularly true where the deploying force is produced bymechanical means such as piston-cylinder arrangements inasmuch as themechanical means must be designed to exert the requisite greaterterminal straightening force and thus must be more robust and heavierthan is required merely for deployment up to the terminal point.Although the unrolling force can be reduced and the terminalstraightening effect thereby rendered easier by reducing the thicknessof the metal forming the deployable nozzle, there is a definite limitwith respect to this thickness wherein buckling of the intermediateconvolution will occur. Although it is possible to approach the problemin this manner and utilize such thin material, it will be necessary toprovide reinforcement for the intermediate convolution to prevent itsbuckling during deployment and thus the weight saving achieved by thethin extension metal is largely offset or may be exceeded by the weightof the anti-buckling means. Accordingly, it is generally more desirableto avoid the necessity for any anti-buckling means and instead to makethe wall thickness of the nozzle extension sufficiently large as. toprevent buckling in the first place. In any case, the problem of radialoffset of the inner fold remains and it would be desirable to removethis problem in many cases.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed toa deployable nozzle in which the above problems are overcome. This isaccomplished by providing an end portion on the inner divergent sectionwhich extends beyond the juncture or attachment between the intermediateconvolution and such inner divergent section and by providing acylindrical band section of the intermediate convolution where it joinsthe inner section. With such an arrangement, it is possible to avoid theradial offset problem and thereby to achieve an extremely smooth jointat the free edge of the inner when the when extension is deployed.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational viewpartly in section illustrating one embodiment of the present invention;

FIG. 2 is an enlarged sectional view illustrating certain details of theinvention during deployment;

FIG. 3 is a view similar to FIG. 2 but illustrating the fully deployedposition;

FIG. 4 is a view similar to FIG. 1 but presenting a further modifiedform of the invention;

FIGS. 5 and 6 illustrate portions of the preferred embodiment of theinvention;

FIG. 7 is a sectional view illustrating certain features of the presentinvention;

FIG. 8 is a sectional view illustrating apparatus for forming a nozzleextension; and

FIG. 9 is a graph illustrating certain relationships of the formingoperation.

DETAILED DESCRIPTION OF THE INVENTION With reference to the embodimentof the invention as is shown in FIG. 1, reference character 10 indicatesgenerally a rocket engine which includes a chamber 12 wherein controlledcombustion takes place for the generation of high mass rate flowcombustion gases, as is well known. As is also conventional, the chamber12 opens onto a restricted throat portion 14 through a convergentsection 16 and there is provided a nozzle portion 18 having a divergentinner surface 20 merging smoothly with the throat 14 as shown.

The deployable portion of the rocket nozzle extension is indicatedgenerally by the reference character 21 and will be seen to consist ofan outer frusto-conical convolution or section 22 having its smallerdiameter end joined along a line of fold 24 to an intermediate,frusto-conical convolution or section 26 which terminates at its smallerdiameter end in a short cylindrical portion 28 having an inturned endportion 30 (see particularly FIG. 2) sandwiched between the end edge ofthe inner section 18 and the inner edge of a free end portion 32 whicheffects a short continuation of the inner divergent section 18. Theseparts are joined together along a line of weld 34 in the manner shown.

The geometry of the device which is such as to achieve the very smoothinner surface for the nozzle and its extension when deployed isindicated in FIGS. 2 and 3. In FIG. 2, it will be seen that the length Lof the cylindrical band portion 28 is such as permits the point A toreach the position shown in FIG. 3 when the device isdeployed so thatsuch point A lies substantially at and in close relation to the bevellededge B of the continuation portion 32 so that no gap and a smoothcontinuation of the inner surface 20 is effected without requiringeither the line of fold at 36 defined between the inner divergentsection 18 and the portion 28 or the traveling line of fold 24" which isformed by rolling of the fold line 24 to be straightened excessively. InFIG. 2, the unrolling action causes the fold 24' of FIG. 1 to travel asis shown at the fold 24' in FIG. 2 as it is approaching the band 28, itbeing appreciated that the rolling will commence preferentially at thefold 24 and not at 36 because less energy is required to roll the largercircular fold 24 than is required to roll the smaller circular fold 36.The force required to cause rolling at an annular fold is a function ofthe angle through which the fold must be rolled, the diameter of thecircular fold line and of the thickness of the material involved andthese factors also determine the radius of the fold produced as ittravels. If the force is obtained by internal pressure, then themagnitude of the available force is a function of the diameter of thecircular fold line squared. Generally speaking, for the same thicknessof material throughout, the larger the diameter of the annular foldline, the larger the roll radius and the easier it is to unroll it willinternal pressure and this accounts for the preferential rolling asabove. As the rolling progresses and the diameter of the circular folddecreases, the traveling fold radius decreases and can be predicted forany particular diameter of the annular fold line Thus, the radius of thefold 24 in FIG. 3 can easily be predicted because the diameter of thecircular fold is known.

From these considerations, it can be shown that the length L of thecylindrical band 28 of the undeployed extension as shown in FIGS. I and2 should be equal (Zr/Tan 0)+1rr where 6 is the one-half angle of thenozzle extension as shown in FIG. 3 and r is the radius of the fold at24" when deployment is completed as shown in FIG. 3. The axial extent ofthe continuation portion 32 to its tip edge B (see FIG. 2) is easilycalculated for any given case and is, in any event, approximately equalto 2r/Tan 0, it being appreciated that the outer face 38 of thecontinuation portion 32 is bevelled so as to lie parallel to the axis ofthe nozzle extension.

An alternative form of construction is shown in FIG. 4. In this Figure,a rocket engine is indicated by the reference character 40 and will beseen to have a divergent section 42 provided with an attachment flange44 by means of which the deployable nozzle extension as sembly indicatedgenerally by the reference character 46 is attachable thereto as bysuitable fasteners, such extension being provided with an attachmentflange 48 as shown. In this form of the invention, the inner convolution50 is uninterrupted through its continuation portion 52 (correspondingto the portion 32 of FIGS. 1-3 and likewise presenting as shown in FIG.4 a bevelled outer face as at 38 in FIG. 2) and the intermediateconvolution 54 merges with the annular cylindrical band portion 56 tointersect the portion 50 and is welded thereat to such section 50 asindicated by the reference character 58. For good seating purposes, theband 56 is provided with an outwardly flared section 60 which surroundsand seats upon a corresponding outer surface portion of the innerconvolution 50.

The outer convolution 62 is once again joined to the intermediatesection 54 along the fold line 64 along which preferential rollingoccurs when the deployment action takes place.

In the case both of the form shown in FIG. 1 and that of FIG. 4, adetachable cover assembly 66 may be employed, being identical in eachcase. As is shown for example in FIG. 4, the cover assembly includes adepressed central section or cup 68 defining a recess 70. This recess isprovided for allowing a maximum saving in space inasmuch as a precedingstage may be nested partially into this recess 70 further to effect acompact system. The cover assembly 66 is peripherally secured to aflange portion 62 and means such as is disclosed in the aforesaidapplication US. Pat. No. 3,71 1,027 assigned in common herewith isemployed to effect detachment of the cover assembly 66 at the requisitetime when the extension assembly has been properly deployed to theposition shown in FIG. 3.

FIGS. 5-8 illustrate a preferred embodiment of the invention and themanner in which it is formed. In FIG. 5, the inner section is indicatedby the reference character 80 and may be formed by shear spinningtechniques from a suitable blank to include a belled or frusto-conicalmain body portion 82 having an annular attachment flange 84 at itssmaller diameter end by means of which the device may be attached to theexit end of a rocket nozzle as in FIG. 4. The outer section 86 isindicated in FIG. 6 and it too preferably is formed by shear spinningtechniques from a suitable blank to provide the belled or frusto-conicalmain body portion 88 having a cylindrical portion 90 at its smallerdiameter end and an annular flange 92 at its larger diameter end. Theflange is responsible for allowing the rolling to start properly, aswill be explained presently.

These two portions of the assembly are joined together as by weldingalong the periphery at 94 as indicated in FIG. 7 with the outer sectioninitially extending forward as indicated by the dash-dot lines,whereafter the outer section is rolled back over the inner sectionultimately to be disposed with relation thereto in the fashion indicatedby the dashed line showing to present the outer convolution 96 and theintermediate convolution comprised of the belled or frusto-conicalsection 98 which merges into the aforementioned cylindrical section 90which is joined to the main body portion 82 of the inner convolution 80.The full line position is intended to show the assembly in partialdeployment.

FIG. 8 illustrates a preferred manner in which the rolling back of theassembly is achieved. As shown, the attachment flange 84 of the innersection 80 is utilized to mount a closure plate 100 whereas the flange92 of the outer section is employed peripherally to secure the outersection to the open end of a chamber or housing member 102, a detachablemounting ring 104 being utilized for this purpose. With the parts thusassembled, the interior of the housing 102 is closed to define apressure fluid chamber into which pressurized fluid such as water isintroduced through the inlet 106 which, due to the pressure of the water108 filling the chamber causes the rolling back as indicated in FIG. 7.A frusto-conical reinforcing member 110 may be employed to back up themain body 88 of the outer section 86 during this procedure in order tostabilize it and positively to prevent the possibility of buckling ofthe section 88 during the rolling back operation.

In devices of this nature, an important consideration is that theextension be self-aligning during the deployment operation and aconfiguration illustrated herein positively effects such self-alignment.

It can be shown that the force required to roll the material along anannular fold line is a function of the ratios D/t and r/! where D is theinside diameter of the annular fold line, r is the inside roll radiusaround which the material bends and t is the thickness of the material;and is also a function of the angle through which the bending occurs.Since the roll-through angle of the belled or frusto-conical section 88is equal to 180 minus the included angle of the core, whereas therollthrough angle of the cylindrical section is the largest rollingpressure requirements during deployment are at the terminal portion ofdeployment when the cylindrical section is being unrolled.

To illustrate the relations between these parameters with respect to theforming operation by the method shown in FIG. 8, reference is had to thegraph of FIG. 9 which illustrates families of curves of rolling pressure(of the hydraulic medium 108) as a function of the dimensionless ratiosD/t and r/t.

The point A shows the pressure required at the commencement of rollingin the assembly of FIG. 8 and the point B shows the pressure required atthe termination of the forming operation. The dashed line extending frompoint B to point C illustrates the further rolling along the conicalsection (that is until the cylindrical section is reached) which resultsduring deployment.

It will be appreciated that the inside roll radius r which results atthat particular point at which the forming operation terminates will besome predictable value dependent upon the material used, its thickness,the roll-through angle, and the inside diameter of the annular fold.Indeed, the inside roll radius may be predicted for any point either onthe conical section or on the cylindrical section so that, as describedin conjunction with FIG. 3, the length of the extension 32 may bedetermined with accuracy.

It will further be appreciated that both during the forming operationand during subsequent deployment, the rolling will proceed underconditions of minimum energy expended by the means which effects therolling. If this means is in the form of internal pressurizing meansboth for forming and later for deployment, it will be seen that theconditions of deployment may be calculated with precision. Thus, thesystem can be designed by very rapid deployment and this represents animportant feature. As a matter of fact, nozzle extensions for full sizeengines are capable of deployment within time periods of but a fractionof a second. In this way, during stage separation, the next-stage enginecan be readied for firing without loss of time.

The self-aligning feature, regardless of the method of deployment,results from the fact that if misalignment were to commence, the leadingportion of the fold requires a greater roll-through angle than at thelagging portion thereby to increase the required rolling force. This isan inherent feature of rolling down (i.e., from the larger to thesmaller end) the conical section which preferential rolling effectoccurs naturally so long as means is not employed to prevent it. That isto say, as will be seen clearly from FIG. 9, rolling commencespreferentially at the largest diameter D section because the leastrolling pressure is required (i.e. rolling pressure decreases as D/tincreases). force.

With internal pressure as the deploying means, an additionalself-aligning effect is obtained due to the fact that the rolling forceis proportional to D and the leading side will have a smaller effectivediameter D which thereby reduces the available rolling fork e.

What is claimed is:

l. A rocket engine nozzle extension for use with a rocket engine havinga combustion chamber discharging to a restricted throat followed by adivergent conical nozzle section terminating in a frusto-conical freeend portion, said extension being deployable from an intially collapsedstate to form an expansion ratioincreasing extension of said divergentconical section, said nozzle extension comprising:

a cylindrical section secured exteriorally to said divergent conicalsection in coaxial surrounding relation thereto and extending forwardlytherefrom toward said combustion chamber;

a frusto-conical intermediate convolution extending divergently andforwardly from said cylindrical section; and

a frusto-conical outer convolution extending divergently and rearwardlyin surrounding relation to said intermediate convoltuion, said outerconvolution being joined to said intermediate convolution along anannular fold;

said cylindrical section being of a diameter sufficiently smaller thanthe diameter of the free end edge of said frusto-conical free endportion and of a length relative to the length of said frusto-conicalfree end portion as to permit said annular fold to roll through saidintermediate convolution and said cylindrical section therebylengthening said outer convolution and causing it to form asubstantially smooth extension of said nozzle section at said free endedge of said frusto-conical free end portion.

2. A rocket nozzle extension as defined in claim 1 including means forcausing said annular fold to roll through said intermediate convolutionand said cylindrical section to deploy the extension.

3. A rocket nozzle extension as defined in claim 2 wherein said meanscomprises a cover detachably fixed to the open end of said outerconvolution.

4. A deployable nozzle for rocket engines comprising, in combination:

an inner section having a divergent inner surface of generally conicalform;

an intermediate convolution surrounding said inner section and having anouter surface diverging in the direction opposite to the divergence ofsaid inner surface and adapted to be deployed into registry with saidinner surface of the inner section with minimal radial offset withrespect thereto;

a cylindrical band joining the smaller end of said intermediateconvolution to said inner section along a circumferential line locatedin spaced relation to the larger diameter free end edge of said innersection;

an outer convolution surrounding said intermediate convolution andhaving a divergent inner surface facing the same direction as the innersurface of said inner section; and

an annular fold section joining the larger diameter end of saidintermediate convolution to the smaller diameter end of said outerconvolution.

S. A deployable nozzle for rocket engines as defined in claim 4 whereinthe free end of said inner section is bevelled to present an outer facesubstantially parallel to and concentric with the axis of said nozzle tointersect said inner surface of the inner section at said free end edge;and the diameter of said cylindrical band being sufficiently smallerthan the diameter of said free end edge and of a length relative to thelength of that portion of said inner section which is beyond saidcylindrical band as to permit said annular fold section to roll throughsaid intermediate convolution and said cylindrical band therebylengthening said outer convolution and causing it to form an extensionof said inner section beginning at said free end edge and with a rolledover portion of said cylindrical band overlying and in closely spacedrelation to said outer face of the free end of said inner section.

6. A deployable nozzle for rocket engines as defined in claim 5 whereinsaid inner section comprises a first frusto-conical portion remote fromsaid free end edge of the inner section and a second frusto-conicalportion attached to and forming a continuation of said first portion.

7. A deployable nozzle for rocket engines as defined in claim 6 and incombination therewith:

a rocket engine having a combination chamber and a restricted throat;

said first frusto-conical portion being integrally joined to said rocketengine and presenting a divergent section from said restricted throat.

8. A deployable nozzle for rocket engines as defined in claim 5 and incombination therewith:

a rocket engine having a combustion chamber and a restricted throat;

said inner section being integrally joined to said rocket engine andpresenting a divergent section from said restricted throat.

9. A deployable nozzle for rocket engines as defined in claim 4 and incombination therewith:

a rocket engine having a combustion chamber and a restricted throat;

said inner section being integrally joined to said rocket engine andpresenting a divergent section from said restricted throat.

10. A deployable nozzle for rocket engines ad defined in claim 4 whereinsaid inner section comprises a first frusto-conical portion remote fromsaid free end edge of the inner section and a second frusto-conicalportion attached to and forming a continuation of said first portion.

1 l. A deployable nozzle for rocket engines as defined in claim 10 andin combination therewith:

a rocket engine having a combustion chamber and a restricted throat;

said frusto-conical portion being integrally joined to said rocketengine and presenting a divergent section from said restricted throat.

12. A rocket engine nozzle extension as defined in claim 1 wherein saidfrusto-conical free end portion terminates in a bevel presenting anouter face substantially parallel to and concentric with thelongitudinal axis of the nozzle extension and which outer faceintersects the inner surface of said free end portion to define saidfree end edge, a rolled over portion of said cylindrical sectionoverlying said' outer face in closely spaced relation thereto when theextension is deployed.

13. A rocket engine nozzle extension as defined in claim 12 wherein saiddivergent conical nozzle portion of the rocket engine comprises a firstfrusto-conical section extending from said restricted throat and asecond frusto-conical section forming a continuation of and attached tosaid first frusto-conical section.

14. A rocket engine nozzle extension as defined in claim 1 wherein saiddivergent conical nozzle portion of the rocket engine comprises a firstfrusto-conical section extending from said restricted throat and asecond frusto-conical section forming a continuation of and attached tosaid first frusto-conical section.

' UNITED STATES PATENT O jFFICE CERTIFICATE OF CORRECTION Patent No. 3,784 ,109 Dated January 8 1974 lnventofls) John Wilbur Doeringer It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 34, "offset" should read "offset" Column 3, line 7, after"inner" insert section same line 7, cancel "when", second occurrence;line 67, "24'" should read 24 Column 4, line 16, "will" should read withline 27, cancel the parentheses; line26, after "be" insert chosen toColumn 5, line 3, cancel "application". Column 6, line 1, "core'fbshouldread cone line 56, cancel "force"; line 61, "fork e" should read force IColumn 8,

line 13, "combination" should read combustion Signed and sealed this24th day of September 1974.

(SEAL) Attest:

MCCOY N. GIBSON JR. v c. MARSHALL 19mm Attesting Officer Commissioner-ofPatents FORM Po-wso (10-69) e usco MM-oc scan-Pen,

u.s. eovtnuurin rnm rmo omcr: 93

1. A rocket engine nozzle extension for use with a rocket engine havinga combustion chamber discharging to a restricted throat followed by adivergent conical nozzle section terminating in a frusto-conical freeend portion, said extension being deployable from an intially collapsedstate to form an expansion ratioincreasing extension of said divergentconical section, said nozzle extension comprising: a cylindrical sectionsecured exteriorally to said divergent conical section in coaxialsurrounding relation thereto and extending forwardly therefrom towardsaid combustion chamber; a frusto-conical intermediate convolutionextending divergently and forwardly from said cylindrical section; and afrusto-conical outer convolution extending divergently and rearwardly insurrounding relation to said intermediate convoltuion, said outerconvolution being joined to said intermediate convolution along anannular fold; said cylindrical section being of a diameter sufficientlysmaller than the diameter of the free end edge of said frustoconicalfree end portion and of a length relative to the length of saidfrusto-conical free end portion as to permit said annular fold to rollthrough said intermediate convolution and said cylindrical sectionthereby lengthening said outer convolution and causing it to form asubstantially smooth extension of said nozzle section at said free endedge of said frusto-conical free end portion.
 2. A rocket nozzleextension as defined in claim 1 including means for causing said annularfold to roll through said intermediatE convolution and said cylindricalsection to deploy the extension.
 3. A rocket nozzle extension as definedin claim 2 wherein said means comprises a cover detachably fixed to theopen end of said outer convolution.
 4. A deployable nozzle for rocketengines comprising, in combination: an inner section having a divergentinner surface of generally conical form; an intermediate convolutionsurrounding said inner section and having an outer surface diverging inthe direction opposite to the divergence of said inner surface andadapted to be deployed into registry with said inner surface of theinner section with minimal radial offset with respect thereto; acylindrical band joining the smaller end of said intermediateconvolution to said inner section along a circumferential line locatedin spaced relation to the larger diameter free end edge of said innersection; an outer convolution surrounding said intermediate convolutionand having a divergent inner surface facing the same direction as theinner surface of said inner section; and an annular fold section joiningthe larger diameter end of said intermediate convolution to the smallerdiameter end of said outer convolution.
 5. A deployable nozzle forrocket engines as defined in claim 4 wherein the free end of said innersection is bevelled to present an outer face substantially parallel toand concentric with the axis of said nozzle to intersect said innersurface of the inner section at said free end edge; and the diameter ofsaid cylindrical band being sufficiently smaller than the diameter ofsaid free end edge and of a length relative to the length of thatportion of said inner section which is beyond said cylindrical band asto permit said annular fold section to roll through said intermediateconvolution and said cylindrical band thereby lengthening said outerconvolution and causing it to form an extension of said inner sectionbeginning at said free end edge and with a rolled over portion of saidcylindrical band overlying and in closely spaced relation to said outerface of the free end of said inner section.
 6. A deployable nozzle forrocket engines as defined in claim 5 wherein said inner sectioncomprises a first frusto-conical portion remote from said free end edgeof the inner section and a second frusto-conical portion attached to andforming a continuation of said first portion.
 7. A deployable nozzle forrocket engines as defined in claim 6 and in combination therewith: arocket engine having a combination chamber and a restricted throat; saidfirst frusto-conical portion being integrally joined to said rocketengine and presenting a divergent section from said restricted throat.8. A deployable nozzle for rocket engines as defined in claim 5 and incombination therewith: a rocket engine having a combustion chamber and arestricted throat; said inner section being integrally joined to saidrocket engine and presenting a divergent section from said restrictedthroat.
 9. A deployable nozzle for rocket engines as defined in claim 4and in combination therewith: a rocket engine having a combustionchamber and a restricted throat; said inner section being integrallyjoined to said rocket engine and presenting a divergent section fromsaid restricted throat.
 10. A deployable nozzle for rocket engines addefined in claim 4 wherein said inner section comprises a firstfrusto-conical portion remote from said free end edge of the innersection and a second frusto-conical portion attached to and forming acontinuation of said first portion.
 11. A deployable nozzle for rocketengines as defined in claim 10 and in combination therewith: a rocketengine having a combustion chamber and a restricted throat; saidfrusto-conical portion being integrally joined to said rocket engine andpresenting a divergent section from said restricted throat.
 12. A rocketengine nozzle extension as defined in claim 1 wherein saidfrusto-coNical free end portion terminates in a bevel presenting anouter face substantially parallel to and concentric with thelongitudinal axis of the nozzle extension and which outer faceintersects the inner surface of said free end portion to define saidfree end edge, a rolled over portion of said cylindrical sectionoverlying said outer face in closely spaced relation thereto when theextension is deployed.
 13. A rocket engine nozzle extension as definedin claim 12 wherein said divergent conical nozzle portion of the rocketengine comprises a first frusto-conical section extending from saidrestricted throat and a second frusto-conical section forming acontinuation of and attached to said first frusto-conical section.
 14. Arocket engine nozzle extension as defined in claim 1 wherein saiddivergent conical nozzle portion of the rocket engine comprises a firstfrusto-conical section extending from said restricted throat and asecond frusto-conical section forming a continuation of and attached tosaid first frusto-conical section.